We have developed and prevalidated an in vitro screening test for phototoxicity, the Enhanced Phototoxicity Assay in Reconstituted Skin (EPARS), to replace the current standard animal phototoxicity tests. The phototoxic potential of chemicals, cosmetics, dietary supplements and Pharmaceuticals are a major and growing concern in the consumer products industry, but society and the government have demanded decreased use of experimental animals. EPARS is more objective, faster, and less expensive than animal tests. To-date, no alternative phototoxicity test has been validated in the U.S. (via ICCVAM), although the 3T3 Neutral Red Uptake (3T3NRU) assay has been accepted in the E.U. after validation by ECVAM. EPARS is significantly superior to the 3T3NRU viability test because it overcomes several of the 3T3NRU test's limitations. Specifically: (1) EPARS is based upon a differentiated tissue model that closely parallels human skin morphology, instead of a fibroblast monolayer; (2) the tissues are composed of primary human keratinocytes in a 3D culture system, a more relevant model than a mouse tumor cell line; and (3) test substances can be applied directly, avoiding the often problematic solubilization of formulations into culture media. If developed to its full potential, EPARS would be the most accurate assay available to identify potential phototoxic agents in humans. We propose to confirm the reproducibility, sensitivity, specificity and predictability of EPARS by testing an expanded list of known phototoxins and validate the most predictive and accurate tissue viability endpoints identified in Phase I. We will also use human gene microarrays to measure changes in gene expression patterns and identify genes that can be used as predictors for induction of phototoxicity. This Phase II work will supplement and strengthen the foundation of EPARS in preparation for submission to U.S. regulatory agencies as an alternative to animal phototoxicity testing. [unreadable] [unreadable]